The present invention relates to a lubricating structure in a scroll compressor such as may be used for an air conditioning unit or low-temperature refrigerating unit.
Prior to describing the invention, the principles of a scroll-type fluid machine will be described briefly.
FIGS. 1A to 1D show the fundamental components of a scroll-type fluid machine used as a compressor and illustrate the operating principles thereof. In FIG. 1, reference numeral 1 designates a stationary scroll; 2, an orbiting scroll; 3, an intake chamber; 4, a discharge port; and 5, compression chambers. Further in FIG. 1, reference character O designates the center of the stationary scroll 1.
The stationary scroll 1 and the orbiting scroll 2 have spiral wraps 1a and 2a which have the same configuration but are wound in opposite directions; that is, they are complementary in configuration. As is well known in the art, the shape of the spiral wraps 1a and 2a is that of an involute curve or arc.
The operation of this scroll compressor will be described. The stationary scroll 1 is held stationary relative to the frame of the machine. The orbiting scroll 2 is combined with the stationary scroll 1 in such a manner that the phase of the former is shifted by 180.degree. from that of the latter. The center of the orbiting scroll 2 moves around the center O of the stationary scroll 1 without the wrap of the orbiting scroll rotating. Relative positions of the stationary scroll 1 and the stationary scroll 2 at orbiting angles of 0.degree., 90.degree., 180.degree. and 270.degree. are indicated in FIGS. 1A to 1D, respectively. When the orbiting scroll 2 is at the 0.degree. position as shown in FIG. 1A, the gas to be compressed is allowed to enter the compression chambers 5 formed between the wraps 1a and 2a. As the orbiting scroll 2 moves, the volumes of the compression chambers 5 are reduced so that the gas contained therein is compressed and finally discharged through the discharge port 4 provided near the center of the stationary scroll 1.
FIG. 2 shows an example of a scroll compressor such as may be used as a refrigerant compressor. In FIG. 2, reference numeral 1 designates a stationary scroll having a wrap 1a formed on one side of a base plate 1b; 2, an orbiting scroll having a wrap 2a on one side of a base plate 2b; 3, a suction inlet of a suction chamber; 4, a discharge port; 5, compression chambers formed between the wraps 1a and 2a when the wraps 1a and 2a are combined together; 6, a main shaft; 7, an oil cap having a suction hole 7a and which is mounted on the main shaft in such a manner that it covers the lower end of the main shaft with a certain clearance between the lower end of the main shaft and the oil cap; 8 and 9, bearing frames; 10, an electric motor rotor; 11, a motor stator; 12, a housing; 13, an Oldhams coupling; 14, a baffle plate; 15, an oil pool at the bottom of the housing 12; 16, a suction pipe; 17, a discharge pipe; and 18, an orbiting scroll bearing rotatably mounted on an orbiting scroll shaft 2c fixed to the side of the base plate 2b opposite the wrap 2a and located eccentrically with respect to the main shaft 6. The orbiting scroll bearing 8 is fitted in an eccentric hole 60a in a large-diameter part 6a forming the upper end portion of the main shaft 6.
Further in FIG. 2, reference numeral 19 designates a first main shaft bearing supporting the cylindrical wall 61a of the large-diameter part 6a of the main shaft 6; 20, a second main shaft bearing supporting a small-diameter part 6b forming the lower end portion of the main shaft 6; 21, a first thrust bearing supporting the lower surface 20b of the base plate 2b of the orbiting scroll 2 in the axial direction; 22, a second thrust bearing supporting, in the axial direction, a step 6c formed between the large-diameter part 6a and the small-diameter part 6b of the main shaft; 23, a lubrication hole formed in the main shaft eccentrically with respect to the central longitudinal axis of the main shaft, the lubrication hole 23 having an opening 23a in the lower end of the main shaft 6 and communicating with the bearings 18 and 20; 24, a vent hole formed in the main shaft 6; 25 and 26, oil return holes in oil passages; and 27 and 28, communicating holes in the inlet gas passages.
With the orbiting scroll 2 combined with the stationary scroll 1, the orbiting scroll shaft 2c is engaged with the main shaft 6 through the orbiting scroll bearing 18, and the orbiting scroll 2 is supported by the orbiting scroll bearing 18 and the first thrust bearing 21 of the bearing frame 8. The main shaft 6 is supported by the first main shaft bearing 19, the second main shaft bearing 20, and the second thrust bearing 22 which are arranged in the bearing frames 8 and 9 which are coupled to each other, for instance, through a faucet-type joint.
The Oldhams coupling 13 is provided between the orbiting scroll 2 and the bearing frame 8 in order to prevent rotation of the wrap of the orbiting scroll 2 and to allow only the orbiting movement of the scroll 2. The stationary scroll 1, together with the bearing frames 8 and 9, is secured with bolts. The motor rotor 10 is fixedly mounted on the main shaft 6 by press fitting, shrink fitting or with screws, and the motor stator 11 is fixedly secured to the bearing frame 9 in the same manner. The oil cap 7 is fixed to the main shaft 6 by press fitting or shrink fitting. The assembly thus formed is mounted in the housing 12 with the scrolls 1 and 2 at the top and the motor rotor 10 and the motor stator 11 at the bottom.
The operation of the scroll compressor thus constructed will be described.
When the motor rotor 10 rotates, the orbiting scroll 2 is moved through the main shaft 6 and the Oldhams coupling 13, and compression in accordance with the operating principle described with reference to FIG. 1 starts. Thereupon, refrigerant gas is sucked through the inlet pipe 16 into the housing 12. This gas, as indicated by the solid-line arrows, passes through the communicating hole 27 between the bearing frame 9 and the motor stator 11 and through the air gap between the motor rotor 10 and the motor stator 11 to cool the motor, and then passes through the communicating hole 28 between the housing 12 and the bearing frames 8 and 9 and is delivered through inlet 3 of the stationary scroll 1 to the compression chambers 5 where it is compressed. The gas thus compressed is discharged through the discharge port 4 and the discharge pipe 17.
Lubricating oil from the oil pool 15 is supplied to the bearings 18 and 20 through the suction hole 7a of the oil cap 7 and the lubrication hole 23 in the main shaft, and to the bearings 21, 19 and 22 from the bearing 18, in the stated order, by the centrifugal pumping action caused by the oil cap 7 on the main shaft 6 and the lubrication hole 23, as indicated by the broken-line arrows. The oil once used for lubrication is returned to the oil pool 15 through the oil return holes 25 and 26 in the bearing frames 8 and 9.
The baffle board 14 is provided to close the gap between the bearing frame 8 and the peripheral surface of the orbiting scroll 2 so that oil which has leaked through the bearing 21, etc. will not be sucked directly into the suction inlet 3. The baffle board 14 and the orbiting scroll 2 separate the suction inlet 3 from the slide mechanism section. The vent hole 24 in the main shaft 6 acts to quickly discharge the gas from the oil cap 7 in operation, thereby increasing the pumping efficiency.
The lubricating structure in the compressor thus constructed will be described in detail with reference to FIG. 3. FIG. 3 is a sectional view showing a part of the structure around the upper end portion of the main shaft.
In FIG. 3, reference numeral 30 designates a first space defined by the lower end face 20c of the orbiting scroll shaft 2c, the orbiting scroll bearing 18, and the bottom 600a of the eccentric hole 60a. Reference numeral 31 designates a second space which is provided on the side of the inner periphery of the thrust bearing 21 and which is defined by the lower surface 20b of the base plate 2 of the orbiting scroll 2 and the upper end face 61a of the large-diameter part 6a of the main shaft 6. Reference numeral 32 designates a third space formed on the side of the outer periphery of the thrust bearing 21. Reference numeral 33 designates a first oil groove formed in the inner wall of the orbiting scroll bearing 18 and extending from a point near the upper end face to the lower end face of the orbiting scroll bearing 18. The lower end of the first oil groove 33 communicates with the first space 30. Reference numeral 34 designates a second oil groove which is on the side of the outer cylindrical surface 61a of the large-diameter part 6a of the main shaft 6 and which is formed in the sliding surface on the main shaft bearing 19. The upper end of the second oil groove 34 is communicated with the second space 31, and its lower end is located near the lower end of the main shaft bearing 19. Reference numeral 35 designates a second lubrication hole through which the first oil groove 33 is communicated with the second oil groove 34. Further, 21a designates a plurality of third oil grooves formed in the sliding surface of the thrust bearing on which the orbiting scroll 2 slides. The third oil grooves 21a communicate with the second space 31, while second ends are communicated through the third space 32 with the oil return hole 25.
As is apparent from the above description, the first lubrication hole 23, the first space 30, the first oil groove 33, the second lubrication hole 35, the second oil groove 34, the second space 31 and the third oil grooves 21 form a series of lubrication paths. The oil pumped by the centrifugal pumping action moves as indicated by the broken line arrows, and then passes to the oil return hole 25 through the third space 32. The remainder of the oil path is as described with reference to FIG. 2.
In the above-described lubricating structure, the lubrication paths are maintained filled with oil during the operation of the compressor. However, when the compressor is stopped, the oil flow by force of gravity in directions opposite to the directions of the broken line arrows in FIG. 3, finally returning to the oil pool 15 through the first lubrication hole 23, with the result that the lubrication paths are filled with gas. Accordingly, when, under this condition, the compressor is again started, the gas is discharged as indicated by the broken line arrows, and then the lubrication paths are filled with oil. Therefore, there is a lag time from the time the compressor is started until all sliding parts are lubricated.
In a scroll compressor in which the compressor section is at the top and the motor section is at the bottom, when, for instance, the compressor is started with refrigerant in the oil pool, the oil in the oil pool 15 may foam momentarily, rising to the upper portion of the housing 12 and not returning to the oil pool 15 immediately. That is, an oil shortage can occur momentarily in the compressor. Accordingly, the bearings and other sliding members can seize or be damaged.